Process for the treatment of hydrocarbon oil



2,075,901 PROCESS FOR THE TREATMENT'YOF HYDROCARBON OIL I s. s. JOHNSON, JR

Filed Aug. 31, 1934 INVENTOR.

JI'ZWIf/Yilrwayde ATTORNEY LOW M WQkTIb Patented Apr. 6, 1937 UNITED STATES PATENT OFFICE PROCESS FOR- THE TREATMENT OF HYDROCARBON OIL Application August 31, 1934, Serial No. 742,240

8 Claims.

This invention relates to processes for the treatment of hydrocarbon oil and pertains more particularly to processes for converting relatively heavy high boiling hydrocarbon oils into lighter products of lower boiling point, such, for example,

as gasoline.

It is an object of my invention to provide an improved process whereby fresh, relatively heavy charging stock, such, for example, as crude pew troleum oil, partially reduced crude or the like,

may be subjected to a preliminary distilling operation to separate lighter from heavier constituents, and whereby these separate constituents may be subjected to suitable cracking steps to produce quantities of light distillate of the final desired boiling range as well as cracking stock suitable for further conversion.

A further object of my invention isto provide an improved process whereby the steps of distilling fresh charging stock, cracking clean gas oil, reforming naphtha, and viscosity breaking reduced crude, may be carried out simply and emciently with a relatively small amount of apparatus.

In accordance with my invention, fresh relatively heavy charging stock such as crude petroleum oil, partially reduced crude or the like, is preheated to a distilling temperature, for example by indirect heat exchange with hot products of subsequent cracking steps, and is then introduced into a distilling zone wherein separation of vapors from liquid residue takes place. The vapors pass into a low pressure fractionating zone wherein constituents heavier than those desired for the final product are condensed, the

fractionated vapors being removed and condensed as a final desired product or as a portion of a final desired product. The reduced crude or liquid residue remaining is Withdrawn and introduced into an evaporating zone in contact with hot cracked vapors and is therein subjected to additional partial vaporization, the vapors passing upwardly through the evaporating zone and. undergoing partial fractionation therein if desired, vapors remaining uncondensed passing off to a high pressure fractionating zone and therein undergoing fractionation to separate heavier constituents from those desired in the final product, the vapors, after fractionation, being condensed and collected in a suitable receptacle. The reflux condensate from the high pressure fractionating zone is removed and passed through a cracking zone wherein it is subjected to conversion, preferably in the vapor phase, and is then introduced into the evaporating zone either with or without previous vapor phase soaking. Liquid residue is withdrawn from the evaporating zone and subjected to flash distillation under low pressure, whereby partial vaporization thereof occurs. The resulting vapors are introduced into the low pressure fractionating zone in contact with the charging stock introduced thereinto, while the unvaporized portions of the liquid residue are separately withdrawn as fuel oil or for any other use desired.

A condensate in the nature of heavy naphtha, and comprising heavy ends of gasoline, is preferably withdrawn from the low pressure fractionating zone and passed through a reforming coil wherein it is raised toa reforming temperature suitable to cause the conversion thereof into relatively high anti-knock gasoline constituents, and the relatively hot products are introduced into the evaporating zone in contact with the other liquids and vapors therein. These reformed products, being of relatively high temperature, materially aid in the efficient viscosity-breaking of the reduced crude introduced into the evaporator, whereby additional quantities of gas oil suitable for cracking are formed. These quantities of gas oil pass over into the high pressure fractionator and are condensed therein as reflux condensate. An additional intermediate 'condensate, heavier than the heavy naphtha condensate, is preferably removed from the low pressure fractionating zone and a portion thereof may be diverted from the process as furnace oil while another portion is introduced into the evaporator and into the high pressure fractionator, if desired, as refluxing medium, which also serves as additional cracking stock.

The distillate formed by condensing the fractionated vapors removed from the low pressure, fractionating zone is preferably in the nature of light gasoline, that is, gasoline free from its heaviest constituents, the latter being removed from the low pressure fractionating zone and passed through the reforming zone for conversion into higher anti-knock products. The distillate removed from the high pressure fractionating zone may, on the other hand, be a gasoline containing both high and low boiling constituents and suitable for use without blending, but preferably the final desired product is formed by blending the light gasoline from the low pressure fractionating zone with the gasoline from the high pressure fractionating zone.

The above-mentioned and further objects and. advantages of my invention, and the manner of obtaining them, will be more fully explained in the following description taken in conjunction with the accompanying drawing.

The single figure of the drawing represents, diagrammatically, an oil cracking system embodying my invention.

Referring more particularly to the drawing, reference numeral I indicates a charging line through which fresh, relatively heavy charging stock is forced by pump 2, this charging stock consisting of crude petroleum oil, partially reduced crude, or the like. The oil passes through indirect heat exchangers 3, 4 and 5, wherein it is raised to a distillation temperature, and is then introduced into the lower portion of the fractionating section 6 of crude flash tower I, wherein it undergoes partial vaporization as the result of contained heat and the direct interchange of heat from the vapors entering the lower portion of the fractionating section of the tower. The vapors pass upwardly through the fractionating column 6, which is under relatively low pressure, the vapors remaining uncondensed at the top of the tower being removed through line 8 and condenser 9, and resulting condensate being collected in receiver III. This condensate will preferably consist of the lighter ends of gasoline but may also include heavier ends. A portion of this condensate is preferably pumped back to the top of the tower through line I I, having pump I2, in the usual manner. Or, cooling may be applied to the column 6 in any other wellknown manner.

A relatively light condensate in the nature of heavy naphtha, and comprising heavier ends of gasoline, is removed from the fractionating tower 6 through line I3, and passed into stripper I4. If desired, stripping of lighter constituents from the condensate may be aided by injecting steam into the stripper I4, through a line not shown, and returning the light ends to the column 6 through line I5 in the well known manner. The condensate is picked up from the base of the stripper I4 and passed through conduit I6 by action of pump I1, if desired in mixture with naphtha from an external source supplied by valved pipe 70, through a reforming coil located in the combination furnace I8 and is therein .raised to temperature suflicient to cause the formation of relatively high anti-knock gasoline constituents, the. resulting hot reformed products being passed through transfer line I9, having control valve 20, into the lower portion of the evaporator tower 2 I.

In the evaporator 2| separation of vapors from liquid takes place, the vapors passing upwardly through the tower and undergoing partial condensation, if desired, by contact with fractionating elements 22, and the use of reflux through line 60 the vapors remaining uncondensed passing off through vapor line 23 into the base of high pressure fractionator 24. In this fractionator the vapors undergo fractionation in the usual well known manner by contact with bubble trays or other suitable fractionating elements, and the fractionated vapors are removed from the top of the tower through vapor line 25, and are condensed in condenser 26, resulting condensate being collected in the gas separator 21. The necessary cooling at the top of the high pressure fractionator 24 is provided by the indirect heat exchanger 3 and an additional cooler, not shown, if desired, to which a condensate withdrawn from an upper trap-out tray in the fractionator, is passed by way of line 28, by action of pump 29. Any other suitable means may be provided for cooling the top of the fractionator 24 as desired.

Reflux condensate collects in the base of the fractionator 24 and is removed therefrom and forced by action of pump 30 through line 3| into a cracking coil located in the furnace I8, wherein the oil is raised to a cracking temperature and subjected to conversion, preferably in the vapor phase, and is then passed through line 32 into the soaking drum 33 wherein it undergoes additional conversion, the resulting hot cracked products being passed through line 34 into the base of the. evaporator 2|, wherein separation of the cracked products into vapors and liquid residue occurs. The soaking drum 33 may be eliminated if desired, the hot cracked products from the cracking coil in that case being passed directly to the evaporator.

Liquid residue is removed from the base of the evaporator 2| and passed through line 35, having pressure reducing valve 36, into the base of crude flash tower I, which is maintained under a. considerably lower pressure than that of the evap 0 rator 2| and wherein separation of the liquid residue into vapors and liquids takes place, as a result of the contained heat thereof. The generated vapors move upwardly through the tower I, those passing above the trap-out tray 3'! being contacted with the fresh heavy charging stock introduced through line I. Unvaporized portions of the liquid residue are withdrawn from the base of the tower I through line 38 and cooler 39 as fuel oil or for any other use desired. A pump 46 may be used if necessary to force the oil through the cooling coil. Condensed portions of the rising vapors and unvaporized portions of the fresh heavy charging stock collect on the trap-out tray 31 and are removed therefrom through conduit M and forced, by action of pump 42, through indirect heat exchanger 43 into the evaporator tower 2I wherein they contact with the rising vapors. If desired on leaving heat exchanger 43 the oil may be subjected to mild viscosity breaking cracking in a furnace coil, not shown, before entering the evaporator. Bafile plates 44 may be provided in the evaporator tower in order to insure thorough contact of the liquid with the rising vapors and to prevent entrainment of heavy liquid particles therein. The oil passing through line 4| into the evaporator tower is heated by indirect heat exchange with liquid residue withdrawn from the base of that tower through pipe 45 and circulated back to the base of the tower, by action of pump 46, through the indirect heat exchangers 43 and 5. This circulation of liquid residue from the base of the evaporator tower serves to provide a temperature control whereby the temperature in the base of the tower may be reduced if necessary.

In the evaporator tower the introduced liquid from the trap-out tray 3'! is subjected to partial vaporization, the vapors passing upwardly through the evaporator tower and to the bubble tower 24, while the liquid travels downwardly and collects in the base of the evaporator tower. The liquid so collected is subjected to a cracking temperature by contact with the introduced hot products from the reforming coil and cracking coil, with the attendant formation of additional products, sufficiently light to vaporize and pass upwardly through the tower and over into the fractionator 24, from which they will be recycled through the cracking coil with the other condensate collected in the base of the fractionator. Those portions of the liquid residue which are not converted into lighter products such as will volatilize and pass overhead in the evaporator tower, are withdrawn through the line 35 and flashed in the base of the tower 1, as described hereinbefore.

An additional intermediate condensate, heavier than the heavy naphtha condensate removed through line I3, is preferably removed from the low pressure fractionating tower 6 through line 41 and is introduced into the stripper 48 wherein any light vapors are separated, these being returned through line 49 to the fractionator 6. The intermediate condensate collected in the base of the stripper 48 may be withdrawn through line 50 as a desired product, but is preferably wholly or in part forced through line by action of pump 52, into the evaporator 2i and fractionator 24, at intermediate points, as a refluxing medium. Portions of the intermediate condensate so introduced into evaporator 2| and fractionator 24 will collect with the reflux condensate in the base of the fractionator and pass through line 3| to the cracking coil. Valves 53 and 54 provide the necessary control. Additional refluxing medium for the fractionator 24 and evaporator 21 may be provided by withdrawing reflux condensate collected on a partial trap-out tray 55 located near the base of the fractionator 24 and passing this condensate through line 56, heat exchanger 4, cooler 57, back to the fractionator and evaporator, under pressure of pump 58. Valved line 59 serves to introduce this cooled reflux into an intermediate point in the fractionator 24 while valved line 30 serves similarly to introduce a portion of this cooled condensate into the top of the evaporator tower 2|. An additional quantity of this cooled reflux condensate may be passed through valved branch line 8| into conduit 34, adjacent the outlet of soaking drum 33, in order to prevent the formation of coke in that line.

The gasoline distillate collected in receiver 2'! may be drawn off through line 62, while that collected in the receiver l0 may be separately withdrawn through line 63. However, distillates from both of these receivers are preferably combined and Withdrawn through a single draw-01f pipe 64, the combination being effected by means of pipe 65. Draw-off line 06 is furnished so that a portion of the reflux condensate formed in the tower 24 may be withdrawn from the process if desired, in order to establish balanced operating conditions.

In carrying out the process the fresh charging stock may be, for example, 35 A. P. I. Midcontinent crude, this being preheated and flashed sufficiently in the crude flash tower 1 so that the liquid withdrawn from the trap-out tray 31 will have a gravity of about 22 A. P. I. The outlet temperature of the naphtha reforming coil in the furnace l8 may be about 950 to 1050 F. and the outlet pressure several hundred pounds per square inch, e. g., 700 pounds per square inch, while the pressure in the evaporator 21 may be considerably less, for example 200 to 300 pounds per square inch, e. g., 250 pounds per square inch. The outlet temperature of the cracking coil may be about 900 to 1050 F. and the pressure about the same as that in the evaporator. The temperature in the base of the evaporator should be as high as possible without deleterious coke formation, this temperature being, for example, not over about 830 F. and preferably not falling below about 800 1". The gasoline distillate collected in the receiver 21 may have an end point of about 437 F., more or less, while the distillate collected in the receiver I0 may have a lower end point of, for example, about 250 to 400 F., more or less. The pressure in the crude flash tower I is considerably lower than that in the evaporator 2i and may be, for example, inthe neighborhood of 15 pounds per square inch.

These figures are given purely by way of example and are not intended in a limited-sense. Other conditions of temperature and pressure may be used in accordance with the teachings of the prior art. These conditions will be dependent upon the character of the charging stock and of the character of the final desired product, but in general it may be said that the cracking of the reflux condensate from the base of the fractionat'or 24 is preferably carried out in the vapor phase under such conditions as to produce a conversion to products in the gasoline boiling range of about 18 to 20%, although higher or lower conversion per pass may be used. The reforming of the heavy naphtha is carried out under such conditions as to form the production of a relatively large quantity, e. g., 75%, of relatively high anti-knock gasoline constituents, and a temperature is maintained in the base of the evaporator tower 2i sufficiently high to insure e'flicient viscosity breaker of the heavy liquid oil introduced thereinto from the flashing zone.

' While I h-ave'described a particular embodiment of my invention for the purposes of illustration, it should be understood that various adaptations and modifications thereof may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. The process of treating hydrocarbon oil which comprises passing a clean distill-ate stock through a cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into an evaporating zone wherein vapors separate from liquid residue, passing resulting vaporsinto a fractionating zone wherein they are subjected to fractionation with the resulting formation of reflux condensate, removing fractionated vapors from said iractionating zone and condensing them as a desired product, removing reflux condensate from said fractionating zone and utilizing it as said clean cracking stock first mentioned, removing liquid residue from said evaporating zone and introducing it into a flashing zone of reduced pressure wherein separation of the residue into vapors and liquid occurs as the result of its contained heat, passing said vapors into a separate low pressure fractionating zone wherein they are separated into light vapors of the desired boiling characteristics, and reflux condensate, removing the fractionated vapors and condensing them as a desired product, introducing fresh, relatively heavy charging stock having naphtha components, into said low pressure fractionating zone for partial vaporization by contact with the hot vapors therein, fractionating resulting vapors with the vapors from the flashed residue, collecting unvaporized portions of the fresh heavy charging stock and condensed portions of the vapors passing through said low pressure fractionating zone, free from unvaporized portions of the flashed residue, and introducing the mixture into said evaporating zone in contact with the hot products therein, removing a light condensate from said low pressure fractionating zone. consisting essentially of heavy naphtha, passing this condensate through a reforming zone wherein it is raised to a temperature suflicient to cause the conversion thereof into relatively high antiknock gasoline constituents, and introducing the resulting highly heated reformed products into said evaporating zone in contact with the hot products from the cracking zone and the unvaporized portions of the heavy charging stock.

2. A process in accordance: with claim 1 wherein an intermediate condensate, heavier than said heavy naphtha condensate, is removed from said low pressure fractionating zone and diverted from the process.

3. A process in accordance with claim 1 wherein an intermediate condensate heavier than said heavy naphtha condensate is removed from said low pressure fractionating zone and introduced into an intermediate point in said evaporating zone as a refluxing medium.

4. A process in accordance with claim 1 wherein an intermediate condensate heavier than said heavy naphtha condensate is removed from said low pressure fractionating zone and introduced into said fractionating zone first mentioned, as a reflux medium.

5. A process in accordance with claim 1 wherein the unvaporized portions of the relatively heavy charging stock and condensed portions of the flashed vapors which are removed from the base of the low pressure fractionating zone, are passed in indirect heat exchange relation with liquid residue withdrawn from said evaporating zone, prior to the introduction of said unvaporized portions of. said fresh heavy charging stock into said evaporating zone.

6. A process in accordance with claim 1 where in said fresh relatively heavy charging stock is, prior to its introduction into said low pressure fractionating zone, brought into indirect heat exchange relation with hot products at the top of said fractionating zone first mentioned, condensate from a lower portion of said fractionating zone first mentioned, and liquid residue withdrawn from said evaporating zone, in the order mentioned.

'7. A process in accordance with claim 1 wherein said mixture of unvaporized portions of fresh charging stock and condensed portions of the vapors passing through said low pressure fractionating zone are passed in counter current contact with the hot vapors rising through said evaporating zone.

8. The process of treating hydrocarbon oil which comprises passing a clean distillate stock through a cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into an evaporating zone wherein vapors separate from liquid residue, passing resulting vapors into a fractionating zone wherein they are subjected to fractionation with the resulting formation of a reflux condensate, removing fractionated vapors from said fractionating zone and condensing them as a desired product, removing reflux condensate from said fractionating zone and utilizing it as said clean cracking stock first mentioned, removing liquid residue from said evaporating zone and introducing it into a flashing zone under reduced pressure, wherein separation of the residue into vapors and liquid occurs as the result of its contained heat, passing said vapors into a separate low pressure fractionating zone wherein they are separated into light vapors of the desired boiling characteristics and reflux condensate, removing the fractionated vapors and condensing them as a desired final product, introducing fresh relatively heavy charging stock into said low pressure fractionating zone for partial vaporization by contact with the hot vapors therein, fractionating resulting vapors with the vapors from the flashed residue, collecting unvaporized portions of the fresh heavy charging stock and condensed portion of the vapors passing through said low pressure fractionating zone, free from unvaporized portions of the flashed residue, and introducing the mixture into said evaporating zone in contact with the hot products therein, removing an intermediate condensate from said low pressure fractio-nating zone, passing it through a separate heating zone wherein it is raised to a cracking temperature and conversion occurs, and introducing the resulting highly heated products of conversion into said evaporating zone in contact with the hot products from the cracking zone and the unvaporized portions of the heavy charging stock.

STEPHEN S. JOHNSON, JR. 

